Virtually all standard profile elements--such as steel studding, fence posts, angle irons, and channel--are shipped and sold in bundles. Within the bundles the shapes of the profile elements are usually exploited by nesting the elements together to reduce package volume and maximize rigidity. Automatic machinery is used to stack and package these elements, since they are bulky and produced in enormous volume for many industrial uses.
Such a stacking machine normally is at the downstream end of a conveyor that feeds the elements to it at a more or less regular rate, with the longitudinal axes of the elements horizontal and perpendicular to the transport direction. As described in German Patent No. 2,106,091 it is known to use a lifter cart and a turning magnet together to deliver turned and unturned successive groups of the elements to a vertically displaceable takeoff cart. The lifter cart drops down to push the elements it carries off onto the takeoff cart. The groups are then pushed off all together so that any gaps between them are closed up.
German Patent No. 2,230,715 describes an apparatus wherein the individual profile elements are transported by carts having combs or racks shaped to hold them in predetermined positions. Turning magnets pick them up and lay them down right side up or upside down, depending on whether they are nested or not, on the takeoff cart.
The efficiency of such a machine is established by the maximum weight it can suitably arrange on the takeoff cart and the speed it can operate with when moving this maximum weight. Obviously with a given workpiece length and cross section, the only factor that can be varied in the stacker is the width of the stack, which is a function of the number of elements handled in each group. Furthermore the machine is rated to work with up to a maximum transfer width, measured parallel to the transport direction, which corresponds roughly to the maximum weight. Thus the machine will be most efficient or productive when it is making packages that have a width equal to the maximum permissible transfer width.
Preferably each package will be a single layer of elements having a package width which is the maximum transfer width. Such a package is normally not stable so that recourse is usually had to parallelepipedal packages of square section perpendicular to the elements.
Since such a package can be very heavy and hold an unmarketably large quantity of the elements, most suppliers normally must therefore put up the bulk of their profile elements in packages that are much smaller than their stackers could productively handle. Nonetheless since such a stacking machine is essential in any large operation in such a size that it can make large rail-freight and similar packages most large suppliers have one large machine. This single large machine is used to make both large packages and small packages. Thus in a standard stacking operation the machine is greatly underutilized..